Nice idea.
I formalized your approach a little by utilizing an extra scriptmodule bashwelcomeextra.sh, which will also "survive" updates of the RetroPie-Setup.
With that the banner looks like this (some info redacted):
bashwelcomeextra.jpg
INSTALLATION
On RetroPie shell as user pi:
cd RetroPie-Setup
mkdir -p ext/local/scriptmodules/supplementary
pushd ext/local/scriptmodules/supplementary
wget -O bashwelcomeextra.sh https://gist.githubusercontent.com/Gemba/bc41f9b2570486b855d6bfa57b3cbdc5/raw/d03b9f101212a0acb37d8750f9006f8639fcc54e/bashwelcomeextra.sh
popd
# remove genuine scriptmodule and install this one
sudo ./retropie_packages.sh bashwelcometweak remove
sudo ./retropie_packages.sh bashwelcomeextra install
# both modules can also be found in the RetroPie-Setup UI in the Configuration/Tools section
# relogon to test or
source ~/.bashrc
Or see gist there